1. (Field of industrial utility)
The present invention relates to a tunneling scanning microscope, particularly to a tunneling scanning microscope which is capable of investigating the surface structure of a material of low electrical conductivity including inorganic compounds, photoconductive organic materials, etc.
2. (Prior arts)
A scanning tunneling microscope is well known in, for example, U.S. Pat. No. 4,343,993. The scanning tunneling microscope is an apparatus with which the surface structure of conductive materials such as metals can be observed in the order of the magnitude of an atom. When a voltage is applied between a conductive material and a conductive tip and they are closely brought together to approx. 1 nm apart, tunneling currents flow therebetween. The tunneling currents change sensitively in response to extremely fine distance changes thereby enabling the observation of the surface structure in the order of the magnitude of an atom. In a tunneling scanning microscope, changes of the tunneling current in response to the change of distances between the conductive tip and the surface of the conductive material have to be large in order to produce a high resolution image of the surface structure of the conductive material. Since higher conductivity of a sample material means higher sensitivity and higher resolution, materials of low conductivity including organic compounds, photoconductive organic materials, inorganic compounds, etc., result in poor resolution or difficulty in surface investigation. Therefore the range of materials applicable to the observation by tunneling scanning microscopes is limited. For example, the surface investigation of organic materials, most of which are of low conductivity, represents such difficulties. Conventionally, the surface image of an organic material is obtained through observing a metal layer which is deposited on the organic materials by evaporation or sputtering. In this case, however, there is a possibility of changes of the surface structure of the organic material during deposition of metal thereon, and therefore investigation without metal deposition has been desired.